Add licenses to all crates, deny dependencies without a license or with an incompatible license (#106)
For this, we're using https://github.com/EmbarkStudios/cargo-deny, which
will check all dependencies transitively for any incompatible/missing
license.
There are other interesting checks in there, but for now this is the
most important.
Co-authored-by: Tobias Koppers <tobias.koppers@googlemail.com>